Evaluation of terrain effect on microwave radiometer measurement and its correction

We develop a new technique for terrain correction of coarse resolution satellite microwave radiometer measurements using the high-resolution digital elevation model (DEM). With the high-resolution DEM and a facet model, we first simulated the terrain influences that resulted from both effects of local incidence and polarization rotation (PR) on the microwave radiometer measurements at the different scales of the radiometer footprints. The emissivity signals of bare surfaces are more sensitive on incidence and PR than vegetated surfaces. So the emissivities at different incidence angles of the bare surface generated by the advanced integral equation model (AIEM) were used to simulate the terrain effects on the satellite measurements. It was found that (1) the PR effect at the satellite footprint can be corrected using the absolute mean PR angle from all facets within the footprint, and (2) the satellite measurements can be described as from a mean incidence angle. Both angles can be obtained from all facets within the footprint with the high-resolution DEM and the satellite viewing geometry. Therefore, a corresponding terrain-correction technique was developed for satellite brightness temperature measurements. We also demonstrate the terrain effects on the satellite measurements from the advanced microwave scanning radiometer-earth observing system (EOS) (AMSR-E).